1. Field of the Invention
The present invention relates generally to digital signal reproducing apparatus, and more particularly to an apparatus of this kind which reproduces a digital signal recorded on a tape by a rotary head.
2. Description of the Prior Art
Recently, PCM tape recorders which convert an audio signal into a pulse code modulated (PCM) signal and record the PCM signal on a tape by the use of a rotary head have been proposed. These tape recorders are referred to, for example, as R-DAT. An apparatus for reproducing the PCM signal needs a tracking controller which reproduces a record tracking signal and then controls the running of the tape so that the rotary head exactly scans tracks on which the signals are recorded.
To scan tracks obliquely formed on the tape by a plurality of rotary heads, without employing an ordinary tracking method of the type which detects a pilot signal for the tracking control, there has been proposed a so-called no-tracking system in which a head scans a tape at an interval narrower than the track interval recorded on the tape to read a signal at a speed more than twice the normal speed.
In the above-mentioned no-tracking system, the waving of a bearing for the rotary shaft of a drum and so on can make not only adjacent tracks different in curvature from each other but can also vary the track width. If the variation in the track width becomes large, mistracking can occur. When a tape in which the track width is varied or mistracking has occurred is reproduced, the output level of the reproduced signal is lowered so that the S/N ratio is also deteriorated. To eliminate such defects, as shown in FIG. 1, rotary heads 3A, 3B are respectively mounted on the periphery of a rotary drum 2 connected to a rotation shaft 1 through a head board (not shown) with a sufficiently small angular distance .theta., e.g. 1.degree., relative to the rotating direction thereof, whereby, as shown in FIG. 2, the heads 3A, 3B are controlled to record signals on tracks Ta and Tb obliquely formed on a magnetic tape MT with an azimuth angle in a manner such that the tracks Ta and Tb are parallel to each other and the track width thereof is constant. This method is described in Japanese Laid-open Patent Publications Nos. 59-2205 and 59-177712.
A problem in such a conventional no-tracking method as mentioned above is that since the rotary heads 3A and 3B contact with the tape substantially at the same time, signals reproduced by the rotary heads 3A and 3B must be simultaneously processed at the reproducing side. It is therefore required to provide at the reproducing side two sets of signal processing circuits, such as demodulating circuits, corresponding to the two rotary heads 3A, 3B, thereby rendering the reproducing circuit arrangement complicated.